FMH EXPANSION JOINTS Hyspan（FMH伸缩缝Hyspan）.pdfVIP

FMH EXPANSION JOINTS FMH EXPANSION JOINTS DESIGN OF BELLOWS DESIGN OF BELLOWS The bellows is the flexible element of an expansion joint consisting of one or more convolutions and the end tan- gents. This element is designed to absorb thermal movements that result from a change in temperature in a piping system. A bellows may also be designed to absorb mechanical movements. The number of convolutions in a bellows is a direct relationship to the amount of thermal or mechanical movement in the piping system, and/or the force necessary to achieve this deflection. The bellows is a very unique component of a piping system. It must be designed strong enough to accommo- date the system design pressure, as well as, flexible enough to accept the design deflections for a calculated number of occurrences, with a minimum resistive force. The system pressure and deflection create the major stresses in a bellows. Typically the deflection stresses are higher than the pressure stresses and are meridional or longitudinal in direction. These stresses are calculated and evaluated in the Standards of the Expansion Joint Manufacturers Association, Inc. or EJMA. The pressure stresses include circumferential (hoop) stress in the bellows tangent as well as the convolutions. EJMA defines the bellows tangent membrane stress due to pressure as S1. The bellows circumferential mem- brane stress due to pressure is designated as S in the EJMA calculations. The tangent stress (S ) and 2 1 circumferential bellows stress (S2) must not exceed the maximum allowable stress, which is set by code or the customer’s specification. There are also meridional pressure stresses that are evaluated in the design of a bellows. The bellows meridion- al membrane stress due to pressure is designated as S3 in the EJMA calculations. The oth